Radio apparatus, method for receiving its signal, method for measuring its filter coefficient, and program for measuring its filter coefficient

ABSTRACT

Corresponding to antennas analog RF circuits are provided and their outputs are converted by A/D converters to digital signals. Subsequent thereto and preceding an adaptive array processing, correction filters are arranged. Each correction filter has a filter coefficient for compensating for a difference between a characteristic of an analog RF circuit corresponding thereto and an ideal circuit characteristic. Thus an error of a characteristic between the analog RF circuits can be compensated for. The series of operations are implemented by software.

TECHNICAL FIELD

[0001] The present invention relates generally to radio apparatuses andtheir signal reception methods and filter coefficient measurementmethods and programs, and particularly to those digitally compensatingfor an error of a characteristic of analog circuits.

BACKGROUND ART

[0002] In recent years in a rapidly developing mobile communicationsystem (the Personal Handyphone System (PHS) for example) there has beenproposed a system in which when a radio base station and a mobileterminal device communicate, the radio base station employs adaptivearray processing to extract a signal received from a specific, desiredmobile terminal device.

[0003] Adaptive array processing is a processing which calculates from asignal received from a mobile terminal device a weight vector formed ofreception coefficients (weights) for respective antennas of the radiobase station and provides adaptive control to accurately extract asignal received from a specific mobile terminal device.

[0004] The radio base station is provided with a reception weight vectorcalculator calculating such a weight vector for each symbol of areceived signal and the calculator provides a processing to converge aweight vector to reduce a square of an error between a sum of complexmultiplications of a received signal and a calculated weight vector, anda known reference signal, i.e., an adaptive array processing convergingdirectivity of reception from a specific mobile terminal device.

[0005] In the adaptive array processing, such weight vector convergenceis provided adaptively for example as time elapses and a signal'selectric wave propagation path varies in characteristics, and a receivedsignal has an interference component, noise and the like removedtherefrom to extract a signal received from a specific mobile terminaldevice.

[0006]FIG. 17 is a functional block diagram for functionallyillustrating an adaptive array processing performed in a radio basestation's digital signal processor (DSP) by software.

[0007] With reference to FIG. 17, the radio base station has a pluralityof antennas, for example four antennas A1-A4 receiving signals frommobile terminal device, respectively. The received signals undergo avariety of analog signal processing, as described hereinafter, in analogRF circuits 1-4 and are converted to digital signals by A/D converters5-8, respectively.

[0008] These digital signals are fed to the radio base station's DSP andthe FIG. 17 block diagram is then followed to provide the adaptive arrayprocessing by software.

[0009] With reference to FIG. 17, the received signals converted by A/Dconverters 5-8 to digital signals form a reception signal vector, whichis in turn fed to multipliers M1-M4, respectively, each at one input,and also to reception weight vector calculator 11.

[0010] Reception weight vector calculator 11 uses an adaptive arrayalgorithm described hereinafter to calculate a weight vector formed ofweights for respective antennas and feeds the weights to multipliersM1-M4, respectively, each at the other input, to provide complexmultiplications thereof by the vector of the signals received from thecorresponding antennas. An adder 9 adds the complex multiplicationstogether, which forms an array output signal.

[0011] The sum of the complex multiplications fed as the array outputsignal is also fed to reception weight vector calculator 11.

[0012] Reception weight vector calculator 11 receives a known referencesignal d(t) previously stored in memory 10 and the signal is used in thecalculation of a weight vector by the adaptive array algorithm.Reference signal d(t) is a known signal common to all users that isincluded in a signal received from a mobile terminal device, and forexample for the PHS it is a section of the received signal thatcorresponds to a preamble (PR) and unique word (UW) configured of aknown bit string.

[0013] Furthermore, reception weight vector calculator 11 receives thearray output signal and the signal is used in the calculation of aweight vector by the adaptive array algorithm.

[0014] The reception weight vector calculator 11 employs Recursive LeastSquares (RLS) algorithm, Sample Matrix Inversion (SMI) algorithm, orother similar adaptive array algorithm.

[0015] The RLS, SMI and other similar algorithms are a well knowntechnique in the field of adaptive array processing, for example asspecifically described by Nobuyoshi Kikuma, Adaptive Signal Processingby Array Antenna, Kagaku Gijutsu Shuppan, pp. 35-49, “Chapter 3 MMSEAdaptive Array.” Accordingly it will not be described.

[0016] Reference will now be made to FIG. 18, which is a schematic blockdiagram showing a specific configuration of analog RF circuit 1 shown inFIG. 17. Analog RF circuits 2-4 are identical in configuration to analogRF circuit 1 and accordingly will neither shown nor described.

[0017] With reference to FIG. 18, analog RF circuit 1 includes anamplifier 1 a amplifying a radio frequency (RF) signal of an RF bandreceived at antenna A1, a frequency mixer 1 b using a local oscillationoutput received from a local oscillator (not shown) to convert infrequency the RF signal of the RF band to a baseband signal of abaseband, a bandpass filter BPF1 c limiting an output of frequencyconverter 1 c in bandwidth, and an amplifier 1 d amplifying a basebandsignal of a baseband output from BPF1 c.

[0018] Strictly, the RF signal of the RF band is initially converted bya first frequency mixer to an intermediate frequency (IF) signal of anIF band and then by a second frequency mixer to a baseband signal of abaseband. In FIG. 18, frequency mixer 1 b represents such first andsecond frequency mixers collectively.

[0019] As can be seen from FIG. 18, analog RF circuits 1-4 are eachconfigured of analog circuit components such as amplifiers 1 a, 1 d,frequency mixer 1 b and filter 1 c. However, because of variations inproduction, the analog RF circuits, configured of the same amplifiers,the same frequency mixer and the same filters, still provide differentfrequency characteristics of phase and amplitude and it is difficult tomatch the characteristics between the analog RF circuits.

[0020] Consequently, analog RF circuits 1-4 of signal streamscorresponding to antennas A1-A4, respectively, would provide differentfrequency characteristics of phase and amplitude.

[0021] More specifically, if antennas A1-A4 receive the same signal,their respective analog RF circuits 1-4 having different frequencycharacteristics output signals having different waveforms. In otherwords, a waveform output through a frequency characteristic of eachanalog RF circuit has distortion relative to that output through anideal characteristic.

[0022] That waveforms output from analog RF circuits 1-4, respectively,have distortion is equivalent to that there exists an interferencecomponent in an input signal for the adaptive array processing.

[0023] Signals of the streams of antennas A1-A4, respectively, havinginterference components therein from the outset would contribute to asignificantly impaired ability of the radio base station employing anadaptive array to reduce the interference components.

[0024] An object of the present invention is therefore to provide aradio apparatus and its signal reception method and filter coefficientmeasurement method and program that can correct distortion in waveformof a received signal by compensating for an error of a characteristicbetween streams of received signals that results from an error of acharacteristic of an analog circuit.

[0025] Another object of the present invention is to provide a radioapparatus and its signal reception method and filter coefficientmeasurement method and program that can provide an enhanced ability toreduce an interference component by adaptive array processing bycompensating for an error of a characteristic between streams ofreceived signals resulting from an error of a characteristic of ananalog circuit, for each stream by means of a digital filter.

DISCLOSURE OF THE INVENTION

[0026] The present invention in one aspect provides a radio apparatususing a plurality of antennas to receive a signal, including: aplurality of analog circuits, a plurality of analog-digital converters,a plurality of filter means, and digital signal extraction means. Theplurality of analog circuits are provided to correspond to the pluralityof antennas to subject signals received at the plurality of antennas,respectively, to an analog signal processing. The plurality ofanalog-digital converters receive signals from the plurality of analogcircuits, respectively, to convert the signals to digital signals. Theplurality of filter means receive the digital signals from the pluralityof analog-digital converters, respectively, to filter the digitalsignals to compensate for distortion in waveform resulting from adifference of a characteristic between the plurality of analog circuits.The digital signal extraction means receives signals from the pluralityof filter means, respectively, to subject the signals to a digitalsignal processing to extract a received signal.

[0027] Preferably the plurality of filter means are each a digitalfilter having a characteristic to compensate for a difference between acharacteristic of the analog circuit corresponding thereto and an idealcircuit characteristic.

[0028] Preferably the digital filter is an FIR filter.

[0029] Preferably the digital signal extraction means is an adaptivearray processing circuit employing an adaptive array processing toextract a received signal.

[0030] The present invention in another aspect provides a method ofreceiving a signal in a radio apparatus having a plurality of antennas,the radio apparatus including a plurality of analog circuits provided tocorrespond to the plurality of antennas to subject signals received atthe plurality of antennas, respectively, to an analog signal processing,and a plurality of analog-digital converters receiving signals from theplurality of analog circuits, respectively, to convert the signals todigital signals. The method includes the steps of: filtering the digitalsignals output from the plurality of analog-digital converters tocompensate for distortion in waveform resulting from a difference of acharacteristic between the plurality of analog circuits; and subjectingthe filtered digital signals to a digital signal processing to extract areceived signal.

[0031] Preferably the step of filtering is digital-filtering accompaniedby a characteristic for compensating for a difference between acharacteristic of the analog circuit corresponding thereto and an idealcircuit characteristic.

[0032] Preferably the step of subjecting is a processing employing anadaptive array processing to extract a received signal.

[0033] The present invention in still another aspect provides a methodof measuring a filter coefficient of a radio apparatus using a pluralityof antennas to receive a signal, the radio apparatus including aplurality of analog circuits, a plurality of analog-digital converters,a plurality of filter means, and digital signal extraction means. Theplurality of analog circuits are provided to correspond to the pluralityof antennas to subject signals received at the plurality of antennas,respectively, to an analog signal processing. The plurality ofanalog-digital converters receive signals from the plurality of analogcircuits, respectively, to convert the signals to digital signals. The aplurality of filter means receive the digital signals from the pluralityof analog-digital converters, respectively, to filter the digitalsignals to compensate for distortion in waveform resulting from adifference of a characteristic between the plurality of analog circuits.The digital signal extraction means receive signals from the pluralityof filter means, respectively, to subject the signals to a digitalsignal processing to extract a received signal. The method includes thesteps of: determining a transmission frequency compensating for afrequency offset in the plurality of antennas; determining asampling-timing allowing a sampling error in the analog-digitalconverter to have an optimal value; and calculating a filter coefficientof the filter means from a signal of the transmission frequencydetermined and the sampling-timing determined.

[0034] Preferably the plurality of filter means are each a digitalfilter having a characteristic to compensate for a difference between acharacteristic of the analog circuit corresponding thereto and an idealcircuit characteristic.

[0035] Preferably the step of determining a transmission frequencyincludes the steps of: allowing a transmit signal of a variabletransmission frequency to be received at the plurality of antennas;measuring a frequency offset of the transmit signal received at theplurality of antennas; and determining a transmission frequency allowingthe measured frequency offset to have no more than a predeterminedvalue. The step of determining a sampling-timing includes the steps of:allowing a transmit signal to be received at the plurality of antennas;sequentially varying a sampling-timing at the analog-digital converter;for each the sampling-timing varied, measuring and storing a samplingerror of a received signal extracted by the digital signal extractionmeans; and determining a sampling-timing allowing the sampling error tobe minimized.

[0036] Preferably the step of calculating a filter coefficient includesthe steps of: allowing a signal of the determined transmission frequencyto be received at each of the plurality of antennas; and subjecting asymbol of the received signal to an adaptive array processing as a tapinput to calculate a filter coefficient corresponding to a respectivetap input.

[0037] Preferably the digital signal extraction means is an adaptivearray processing circuit employing an adaptive array processing toextract a received signal.

[0038] The present invention in still another aspect provides a methodof measuring a filter coefficient of a radio apparatus using a pluralityof antennas to receive a signal, the radio apparatus including aplurality of analog circuits, a plurality of analog-digital converters,a plurality of filter means, and digital signal extraction means. The aplurality of analog circuits are provided to correspond to the pluralityof antennas to subject signals received at the plurality of antennas,respectively, to an analog signal processing. The plurality ofanalog-digital converters receive signals from the plurality of analogcircuits, respectively, to convert the signals to digital signals. Theplurality of filter means receive the digital signals from the pluralityof analog-digital converters, respectively, to filter the digitalsignals to compensate for distortion in waveform resulting from adifference of a characteristic between the plurality of analog circuits.The digital signal extraction means receives signals from the pluralityof filter means, respectively, to subject the signals to a digitalsignal processing to extract a received signal. The method includes thesteps of: determining whether a signal received from a mobile terminalat the plurality of antennas satisfies a predetermined condition;holding a signal received from a mobile terminal at the plurality ofantennas, the mobile device satisfying the predetermined condition; andcalculating a filter coefficient of the filter means of the signalreceived and held.

[0039] Preferably the plurality of filter means are each a digitalfilter having a characteristic to compensate for a difference between acharacteristic of the analog circuit corresponding thereto and an idealcircuit characteristic.

[0040] Preferably the step of calculating a filter coefficient includesthe step of subjecting a symbol of the held, received signal to anadaptive array processing as a tap input to calculate a filtercoefficient corresponding to a respective tap input.

[0041] Preferably the digital signal extraction means is an adaptivearray processing circuit employing an adaptive array processing toextract a received signal.

[0042] The present invention in still another aspect provides a programto measure a filter coefficient of a radio apparatus using a pluralityof antennas to receive a signal, the radio apparatus including aplurality of analog circuits, a plurality of analog-digital converters,a plurality of filter means, and digital signal extraction means. Theplurality of analog circuits are provided to correspond to the pluralityof antennas to subject signals received at the plurality of antennas,respectively, to an analog signal processing. The plurality ofanalog-digital converters receive signals from the plurality of analogcircuits, respectively, to convert the signals to digital signals. Theplurality of filter means receive the digital signals from the pluralityof analog-digital converters, respectively, to filter the digitalsignals to compensate for distortion in waveform resulting from adifference of a characteristic between the plurality of analog circuits.The digital signal extraction means receives signals from the pluralityof filter means, respectively, to subject the signals to a digitalsignal processing to extract a received signal. The program causes acomputer to effect the steps of: determining whether a signal receivedfrom a mobile terminal at the plurality of antennas satisfies apredetermined condition; holding a signal received from a mobileterminal at the plurality of antennas, the mobile device satisfying thepredetermined condition; and calculating a filter coefficient of thefilter means of the signal received and held.

[0043] Preferably the plurality of filter means are each a digitalfilter having a characteristic to compensate for a difference between acharacteristic of the analog circuit corresponding thereto and an idealcircuit characteristic.

[0044] Preferably the step of calculating a filter coefficient includesthe step of subjecting a symbol of the held, received signal to anadaptive array processing as a tap input to calculate a filtercoefficient corresponding to a respective tap input.

[0045] Preferably the digital signal extraction means is an adaptivearray processing circuit employing an adaptive array processing toextract a received signal.

[0046] Thus in accordance with the present invention in a radioapparatus a plurality of filter means digitally compensating for adifference of a characteristic between a plurality of analog circuitssubjecting a signal received at a plurality of antennas to an analogprocessing can be provided subsequent to a corresponding analog-digitalconverter so that the digital signal extraction means can receive aninput without an interference component existing therein.

[0047] Furthermore in accordance with the present invention a pluralityof filter means digitally compensating for a difference of acharacteristic between analog circuits can be provided with a filtercoefficient accurately determined for example prior to shipment of aradio apparatus under a condition with a frequency offset corrected anda timing of sampling corrected.

[0048] Furthermore in accordance with the present invention a pluralityof filter means digitally compensating for a difference of acharacteristic between analog circuits can be provided with a filtercoefficient accurately determined for example in a shipped radioapparatus by selecting a satisfactory signal received from a mobileterminal and using the selected signal for calculation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In the drawings:

[0050]FIG. 1 is a functional block diagram showing a configuration of asystem of a radio base station in accordance with the present inventionin a first embodiment;

[0051]FIG. 2 is a block diagram showing a configuration of thecorrection filter shown in FIG. 1;

[0052]FIG. 3 is a flow chart of an operation of the radio base stationin the first embodiment shown in FIG. 1;

[0053]FIG. 4 is a schematic block diagram showing a configuration of asystem in accordance with the present invention in a second embodimentfor measuring a filter coefficient before shipment of a radio basestation;

[0054]FIGS. 5 and 6 are flow charts of first and second halves,respectively, of an operation employing the FIG. 4 system configurationin the second embodiment to measure a filter coefficient beforeshipment;

[0055]FIG. 7 is a schematic block diagram showing a configuration of asystem in accordance with the present invention in a third embodimentfor measuring a filter coefficient after shipment of a radio basestation;

[0056]FIG. 8 is a flow chart of an operation employing the FIG. 7 systemconfiguration in the third embodiment to measure a filter coefficientafter shipment;

[0057]FIG. 9 is a functional block diagram showing a configuration of asystem of a radio base station in accordance with the present inventionin the second or third embodiment for measuring a filter coefficient;

[0058]FIGS. 10-12 are flow charts of first to third stages,respectively, of an operation employing the FIG. 9 system configurationin the second or third embodiment to measure a filter coefficient;

[0059]FIG. 13 is a flow chart of an exemplary variation of the thirdstage of the operation represented in FIG. 12;

[0060]FIG. 14 is a block diagram showing a configuration of an adaptivearray for calculating a tap coefficient;

[0061]FIG. 15 is a block diagram showing a state of the FIG. 14 adaptivearray starting to calculate a tap coefficient;

[0062]FIG. 16 is a schematic diagram for illustrating a concept of aprinciple of determination of a timing of reception in the secondembodiment;

[0063]FIG. 17 is a functional block diagram showing a configuration of asystem of a radio base station as conventional; and

[0064]FIG. 18 is a block diagram showing a configuration of an analog RFcircuit shown in FIG. 17.

BEST MODES FOR CARRYING OUT THE INVENTION

[0065] Hereinafter the present invention in embodiments will bedescribed with reference to the drawings more specifically. In thefigures, like components are denoted by like reference characters.

[0066] First Embodiment

[0067]FIG. 1 is a functional block diagram representing a configurationof a system of a radio base station in accordance with the presentinvention in a first embodiment, in particular for illustratingfunctionally a processing effected by a DSP of a radio station bysoftware.

[0068] The configuration of the radio base station shown in FIG. 1 isidentical to that of the conventional radio base station shown in FIG.17, except the following:

[0069] At a stage subsequent to A/D converters 5-8 and precedingadaptive array processing provided by the DSP (not shown) there areinserted correction filters 12-15 each configured of a digital filter.

[0070] Correction filters 12-15 are each a digital filter having acharacteristic (a filter coefficient, i.e., a tap coefficient)compensating for a difference between a circuit characteristic (e.g.,frequency characteristic of phase and amplitude) of a corresponding oneof analog RF circuits 1-4 and a predetermined, ideal circuitcharacteristic.

[0071] The correction filters having such a characteristic that areinserted in the four signal streams corresponding to antennas A1-A4 cancompensate for an analog circuit characteristic error between thestreams and correct distortion in waveform included in an input signalof each signal stream. As a result, an ability in the subsequentadaptive array processing to reduce an interference component can beenhanced.

[0072]FIG. 2 is a block diagram showing a specific configuration of oneof correction filters 12-15 of FIG. 1 that corresponds to a signal type.Note that correction filters 12-15 are identical in configuration.

[0073] The correction filter shown in FIG. 2 is configured as a wellknown, Finite-Duration Impulse Response (FIR) filter as one example of adigital filter.

[0074] With reference to FIG. 2, samples T of a received signal of asignal stream corresponding to an antenna are sequentially input to ashift register formed of 2N cascaded registers Rs, each holding onesample sequentially, wherein N represents a positive integer. 2Nregisters Rs are provided with 2N+1 inputs/outputs, which correspond to2N+1 samples (referred to as tap outputs) x(t+N), x(t+N−1), . . . ,x(t+T), x(t), x(t−T), . . . , x(t−N+1), x(t−N) fed to 2N+1 multipliersMs, respectively, each at one input.

[0075] 2N+1 multipliers Ms have their respective other inputs receivingfrom a memory (not shown) filter coefficients (also referred to as tapcoefficients) W_(N), W_(N−1), . . . , W₁, W₀, W⁻¹, . . . , W_(−N+1),W_(−N) corresponding to 2N+1 weight information unique to the correctionfilter.

[0076] 2N+1 multipliers Ms multiply the 2N+1 tap outputs by the 2N+1 tapcoefficients and the resultant multiplications are added together by anadder AD and output as an output signal y(t) of the correction filter.

[0077] Note that the 2N+1 tap coefficients input to 2N+1 multipliers Ms,respectively, at their respective other inputs are set to compensate foran error of a characteristic between the signal streams. How a tapcoefficient is determined will be described hereinafter morespecifically.

[0078]FIG. 3 is a flow chart of a basic operation of the radio basestation in the first embodiment shown in FIG. 1.

[0079] With reference to FIG. 3, received signals of the signal streamscorresponding to antennas A1-A4 of FIG. 1 are each digitally filtered bya corresponding correction filer using a filter coefficient (a tapcoefficient), held in a memory (not shown), of the corresponding signalstream (compensation for an error of a characteristic) (step S1).

[0080] The received signal having filtered is then subjected to theadaptive array processing by multipliers M1-M4, adder 9, memory 10 andreception weight vector calculator 11 to effect a normal receptionprocess (step S2).

[0081] Thus in the first embodiment, as shown in FIGS. 1-3, in a radiobase station a plurality of correction filters (digital filters)digitally compensating for a difference of a frequency characteristicbetween a plurality of analog RF circuits are provided at a stagesubsequent to corresponding analog/digital converters and precedingadaptive array processing to prevent an input signal of the adaptivearray processing from having an interference component therein. Anability to reduce an interference component by the adaptive arrayprocessing can be enhanced.

[0082] Second Embodiment

[0083] The filter coefficients (tap coefficients) of correction filters12-15 used in the radio base station of the first embodiment aremeasured (determined), as described hereinafter.

[0084] The filter coefficient can be measured in a factory beforeshipment of the radio station or automatically measured in the shippedradio base station in operation.

[0085] Initially as the second embodiment a filter coefficientmeasurement effected before shipment of the radio base station will bedescribed.

[0086]FIG. 4 is a schematic block diagram showing a configuration of asystem in the second embodiment for measuring a filter coefficientbefore the radio base station is shipped.

[0087] With reference to FIG. 4, to measure a filter coefficient beforeshipment, a signal generator (SG) 40 generates a burst modulation signaland a 4-distributor 50 distributes the generated burst modulation signalto four which are in turn fed through cables, respectively, to a radiobase station 20 at four antennas (not shown). Between radio base station20 and SG40 clocks are synchronized to stabilize operation.

[0088] A personal computer for control (hereinafter referred to as acontrol PC) 30 receives from radio base station 20 a variety of signalsdescribed hereinafter, and generates and applies control signals toradio base station 20 and SG40.

[0089] In the second embodiment a filter coefficient is measured in afactory before shipment. As such, previously the radio base station'sfrequency offset can be compensated for and a processing optimizing asampling error can also be effected as a previous processing beforeunder an ideal condition the filter coefficient measurement can beperformed.

[0090] As a first stage of the previous processing, a frequency offsetis compensated for, as described hereinafter. Initially, from SG40 aburst modulation signal of a transmission frequency set by control PC30is provided through 4-distributor 50 to radio base station 20 at thefour antennas.

[0091] Radio base station 20, having been notified of a previously settransmission frequency from control PC30, measures a frequency offsetcorresponding to an offset between a received signal array-receivedthrough the four antennas and the known transmission frequency andprovides a resultant measurement to control PC30.

[0092] Control PC30 generates a control signal which controls SG40 tochange the transmission frequency of the burst modulation signal tocompensate for the frequency offset.

[0093] Radio base station 20 again measures a frequency offset in areceived signal array-received through the four antennas and provides aresultant measurement to control PC30. The control PC further controlsthe transmission frequency of SG40 to compensate for the frequencyoffset. The compensation as described above is repeated until a measuredfrequency offset attains no more than a predetermined value (for exampleof ±10 Hz). When a decision is made that the frequency offset hasattained no more than the predetermined value the current frequency ofSG40 is determined as a transmission frequency.

[0094] Then, as a second stage of the previous processing, a samplingerror is optimized, as described hereinafter. Initially, from SG40 aburst modulation signal is provided through 4-distributor 50 to radiobase station 20 at the four antennas.

[0095] Radio base station 20 subjects the received signal array-receivedat the four antenna to adaptive array processing to extract a receivedsignal and measures its mean square error (MSE) and provides it tocontrol PC30.

[0096] Control PC30 generates a control signal which controls radio basestation 20 to sequentially change a timing of sampling at A/D converters(A/D converters 5-8 of FIG. 1) in radio base station 20.

[0097] Radio base station 20 again measures an MSE of a received signalat the changed timing of sampling and provides a resultant measurementto control PC30. Control PC30 further changes the timing of sampling inthe radio base station, while the current received signal's MSE ismeasured to hold an MSE corresponding to a timing of sampling.

[0098] The MSE measurement as described above is performed within apredetermined range of timing of sampling and when an MSE attains nomore than a predetermined value the current timing of sampling is held.

[0099]FIG. 16 schematically illustrates a principle of such optimizationof a timing of sampling (a timing of reception). As has been describedabove, after a frequency offset value is optimized, in radio basestation 20 a timing of sampling is assigned, as appropriate, (at fivepoints for example) and for each assignment an MSE is measured andstored in memory.

[0100] Then, as shown in FIG. 16, when an MSE attains no more than apredetermined reference value (for example of 0.1) and also attains aminimal value, the current timing of reception (the timing correspondingto the third point in FIG. 16) is determined as an optimal timing ofreception. Note that the FIG. 16 example shows that measurement of theMSE at the fourth point reveals that the third point corresponds to aminimum value. Accordingly, measurement at the fifth point would nolonger be required.

[0101] The compensation of a frequency offset and the correction of atiming of sampling as described above are further repeated forconfirmation, since a frequency offset value having converged at anoptimal value can be changed by adjusting a timing of reception.

[0102] Thereafter, as has been described above, a burst modulationsignal of a transmission frequency with a frequency offset compensatedfor is applied from SG40 to radio base station 20. In radio base station20 a received signal is sampled at an optimized timing.

[0103] Under such a condition, a filter coefficient of a correctionfilter (correction filters 12-15 of FIG. 1) of radio base station 20 ismeasured.

[0104]FIGS. 5 and 6 together form a flow chart of an operation employingthe FIG. 4 system configuration in the second embodiment to measure afilter coefficient before shipment.

[0105] With reference to FIGS. 5 and 6, a parameter I is set to be 0(step S1). Parameter I represents a frequency of repetition of theprevious processing formed of the two steps of compensating for afrequency offset and correcting a timing of sampling.

[0106] Then control PC30 sets a transmission frequency of a burstmodulation signal generated by SG40 and instructs radio base station 20to array-receive the burst modulation signal at the four antennas andmeasure a frequency offset provided by the antenna. Radio base station20 responsively array-receives the burst modulation signal from SG40,measures a frequency offset at the antenna, and transmits a resultantmeasurement to control PC30 (step S12).

[0107] If control PC30 does not determine that the antenna's measuredfrequency offset is no more than a predetermined value (for example of±10 Hz) (step S13) control PC30 resets the transmission frequency of theburst modulation signal generated by SG40, to compensate for thefrequency offset measured in base station 20 (step S14).

[0108] If control PC30 determines that the antenna's measured frequencyoffset is no more than the predetermined value (for example of +10 Hz)(step S13) then control PC30 maintains the current transmissionfrequency of SG40, while it terminates the first step of the previousprocessing of the filter coefficient measurement (the compensation for afrequency offset) and shifts to the second stage thereof (the correctionof a timing of sampling).

[0109] Initially, control PC30 instructs base station 20 to set a timingof reception (a timing of sampling at A/D converters 5-8 of FIG. 1) tobe an appropriate timing. Radio base station 20 responsivelyarray-receives a burst modulation signal from SG40, measures an MSEindicating a directivity convergence level in a received signal, andtransmits a resultant measurement to control PC30. Control PC30 holdsthe current timing of sampling and the measured MSE value (step S15).

[0110] Control PC30 then instructs base station 20 to increment thetiming of reception (the timing of sampling) by one (step S16).

[0111] Radio base station 20 responsively array-receives a burstmodulation signal from SG40, measures an MSE in a received signal, andtransmits a resultant measurement to control PC30. Control PC30 holdsthe current timing of sampling and the measured MSE value (step S17).

[0112] A decision is then made as to whether the measured MSE has nomore than a predetermined value and also is a minimal value (step S18).If not, control PC30 instructs base station 20 to further change thetiming of reception (the timing of sampling) (step S19) and repeats thestep S17 operation.

[0113] If at step S18 a decision is made that the MSE has no more thanthe predetermined value and has also attained a minimum value, controlPC30 maintains the current timing of sampling in base station 20, whileit terminates the second stage of the previous processing of the filtercoefficient measurement (the correction of a timing of sampling) and adecision is made as to whether parameter I has attained a predeterminediteration (step S20).

[0114] If at step S20 the set iteration has not yet been attained, thenat step S21 parameter I is incremented by one and the above describedfirst stage of the previous processing (steps S12-15) and the secondstage of the previous processing (steps S16-19) are repeated.

[0115] If at step S20 a decision is made that parameter I exceeds theset iteration, then at step S22 control PC30 instructs base station 20to measure an optimal filter coefficient (tap coefficient). Accordingly,SG40 is instructed by control PC30 to generate a burst modulation signalof a transmission frequency provided when a frequency offset attains nomore than a predetermined value, and base station 20 samples this signalat an optimized timing.

[0116] At step S22, from a signal array-received by base station 20under such a condition as above a correction filter's optimal filtercoefficient (tap coefficient) is calculated and a resultant calculationis held in a memory, a flash memory for example (not shown). Thecalculated filter coefficients are fed as a corresponding correctionfilter's tap coefficients W_(N), W_(N−1), . . . , W₁, W₀, W⁻¹, . . . ,W_(−N+1), W_(−N) to the correction filter's multipliers Ms to providefiltering for compensating for an error of a characteristic betweensignal streams. The calculation of a tap coefficient of a correctionfilter will be described later.

[0117] Thus in the second embodiment a plurality of correction filters(digital filters) can be provided with filter coefficients accuratelydetermined for example prior to shipment of a radio apparatus under anideal condition with a frequency offset compensated for and a timing ofsampling corrected, so that distortion of an input waveform can moreaccurately be compensated for.

[0118] Third Embodiment

[0119] As has been described above, filter coefficients can be measuredin a radio base station having been shipped from a factory and inoperation. More specifically, even if before shipment the methoddescribed in the second embodiment is employed to measure filtercoefficients in the factory precisely, after the installation as ananalog RF circuit has its parts altering over years and the environmentalso changes, an error of a characteristic between signal streams canchange. Accordingly, it is necessary to re-measure filter coefficients(tap coefficients) of a correction filter of the base station regularlyat intervals corresponding to a period of time (once a year forexample).

[0120]FIG. 7 is a schematic block diagram showing a configuration in thethird embodiment for measurement of a filter coefficient after the radiobase station is shipped.

[0121] With reference to FIG. 7, after the shipment it is impossiblethat control PC30 and SG40 are prepared and by a signal of a knowntransmission frequency a direct array reception is effected, as has beendescribed with reference to FIG. 4 in measurement prior to shipment.

[0122] Accordingly, after the shipment the previous processing forfilter measurement (i.e., the compensation for a frequency offset andthe correction of a timing of sampling) cannot be performed.Accordingly, base station 20 of interest communicating with a mobileterminal 60 receives a signal therefrom at antennas A1-A4 and of thereceived signals a signal of high precision that satisfies apredetermined condition is selected as a signal having undergone such aprevious processing as described above and from the signal filtercoefficients are calculated.

[0123] The above predetermined condition includes that: (1) a frequencyoffset is no more than a predetermined value (for example of 10 Hz); (2)an MSE indicating a directivity convergence level is no more than apredetermined value (for example of 10⁻⁴) (i.e., there is not asubstantial sampling error); (3) a reception level has a value within apredetermined range (for example of 40 to 60 dBuV) (i.e., there is notsubstantially unnecessary signal distortion); (4) in the slot ofinterest in communication a U-wave level has no more than apredetermined value (for example of 10 dBuV) (i.e., interferencecomponent is significantly row); and (5) a received signal having beendemodulated does not have an reception error, and a received signalsatisfying all or at least a portion of these conditions or criteria isused as a signal for the filter coefficient calculation.

[0124]FIG. 8 is a flow chart of an operation employing the FIG. 7configuration in the third embodiment to measure a filter coefficientafter shipment. Note that the operation illustrated in the FIG. 8 flowchart can be implemented by a program availably downloaded through anetwork by a DSP of an installed base station.

[0125] Initially a decision is made whether there is a signal receivedfrom a user's terminal communicating with the base station of interestthat satisfies the above described, predetermined condition (criterion)(step S31).

[0126] Then, a received signal determined at step S31 to satisfy thecriterion has a frame's signal stored in memory for later filtercoefficient calculation (step S32).

[0127] Then at an appropriate timing, for example when the user is notcommunicating or communication services are stopped, the received signalstored in memory is used to calculate a correction filter's optimalfilter coefficient (tap coefficient) and store a resultant calculationto memory (not shown) (step S33).

[0128] The calculated filter coefficients are fed as a correspondingcoefficient filter's tap coefficients W_(N), W_(N−1), . . . , W₁, W₀,W⁻¹, . . . , W_(−N+1), W_(−N) to the correction filter's multipliers toeffect filtering for compensating for an error of a characteristicbetween signal streams. The calculation of the tap coefficients of thecorrection filter will be described later.

[0129] Thus in the third embodiment a plurality of correction filters(digital filter) can have filter coefficients accurately determined evenin a shipped, operating radio apparatus by selecting a satisfactorysignal received from a mobile terminal and using the signal forcalculation so that distortion of an input waveform can more accuratelybe compensated for.

[0130] Hereinafter the calculation of a filter coefficient (tapcoefficient) in the second and third embodiments will be described.

[0131]FIG. 9 is a functional block diagram showing a configuration of asystem of a radio base station that is necessary in the second or thirdembodiment for measuring a filter coefficient. The FIG. 9 configurationis implemented by a DSP by software.

[0132] In measuring a filter coefficient, a signal for one framereceived from SG40 of FIG. 4 or terminal 60 of FIG. 7 at antennas A1-A4is fed to a synchronization circuit 150 collectively representing acircuit configuration of A/D converters 5-8 of FIG. 1 that is involvedin determining a timing of sampling. Synchronization circuit 150provides a reception weight vector calculation and receive signal sampledevice 110 with synchronization position information regarding a timingof sampling. This information is used in the aforementioned correctionof a timing of sampling.

[0133] On the other hand, a received signal via synchronization circuit150 is fed to multipliers M1-M4 for adaptive array processing and alsoto reception weight vector calculation and receive signal sample device110, and the received signal's frequency offset is calculated and storedto a memory 120. This information is used in the aforementionedcompensation for a frequency offset.

[0134] The received signal output from adder 9 by the adaptive arrayprocessing is fed to a receive signal evaluation device 140 and alsodemodulated by a demodulation circuit 100 to bit data. Demodulationcircuit 100 provides a demodulated output which is in turn exactly fedand also output to receive signal evaluation device 140.

[0135] Receive signal evaluation device 140 receives a signal beforedemodulation by demodulation circuit 100, measures an MSE (a samplingerror) and determines whether a predetermined criterion is satisfied,and it also receives the signal having been demodulated by demodulationcircuit 100 and determines whether the demodulated signal has anreception error. If these decisions reveal that the received signalsatisfies the predetermined criterion an OK signal is generated and ifnot then an NG signal is generated and output to reception weight vectorcalculation and receive signal sample device 110. The received signalfor one frame is held in memory 120 via reception weight vectorcalculation and receive signal sample device 110 and if a decision ismade that the received signal satisfies the above describedpredetermined criterion then the signal is fed to a tap coefficientcalculation device 130 of the present invention.

[0136] Hereinafter from a received signal tap coefficients arecalculated by tap coefficient calculation device 130.

[0137]FIGS. 10-12 together provide a flow chart of an operationemploying the FIG. 9 system configuration in the second or thirdembodiment to measure a filter coefficient.

[0138] In the following description, four antennas are used and acorrection filter (digital filter) serving as a subject is provided withnine taps.

[0139] With reference to FIG. 10 a parameter ANT is set to be 0 (stepS41). Parameter ANT designates an antenna signal stream corresponding toa correction filter for which filter coefficients should be calculated(step S41).

[0140] Then, nine tap coefficients to be calculated are initialized forexample to be 0 (step S42).

[0141] Then, parameter I is set to be 0 (step S43). Parameter Idesignates a number of repetition of a filter coefficient calculation.

[0142] Then, a counter Symbol counting the number of symbols of areceived signal is set to be four (step S44).

[0143] Basically, the configuration calculating a sum of multiplicationsof tap outputs by tap coefficients of such a digital filter (an FIRfilter) as shown in FIG. 2 is analogous to a configuration calculating asum of multiplications of input signals by a weight vector for adaptivearray processing.

[0144] Furthermore, the tap coefficients are calculated so that they areupdated to reduce a difference between a received signal filtered by adigital filter and output therefrom and an output of a filter having anideal filtering characteristic. Such a calculation principle is aprinciple similar to an adaptive array converging a reception weightvector.

[0145] More specifically, FIG. 14 is a block diagram showing aconfiguration of an adaptive array for calculating a tap coefficient.The FIG. 14 configuration corresponds to the configuration of thedigital filter shown in FIG. 2 plus the following:

[0146] More specifically, when y(t) represents a filter outputcorresponding to a sum of multiplications output from an adder AD andd(t) represents a known reference signal stored in memory (memory 10 ofFIG. 9), an error signal e(t)=y(t)−d(t) is calculated by an adder AD2and fed to an MSE calculation circuit 16.

[0147] MSE calculation circuit 16 calculates an MSE of error signal e(t)and the adaptive array changes a weight (a tap coefficient), asappropriate, to minimize the MSE.

[0148] As such, a digital filter for example with nine taps can beregarded as an adaptive array with nine input streams, and such anadaptive array will be referred to as a 9-tap adaptive array for thesake of convenience.

[0149] In the embodiments of the present invention a signal of one frameof a received signal is used to calculate filter coefficients. The factthat there are nine taps, as described above, means that a symbol number4 serving as a center, and the preceding (past) four symbols and thefollowing (future) four symbols for a total of nine symbols are set astap inputs.

[0150]FIG. 15 is a block diagram of the FIG. 14 adaptive array when atap coefficient calculation starts. By entering the t of the center tapoutput x(t) of FIG. 14 from 4T (x(4T) of FIG. 15), a signal x(0T) entersthe most rightward tap and a signal x(8T) enters the most leftward tap.Thus a filter output of y(4T) is obtained. Accordingly in step S44counter Symbol counting the number of symbols of a received signal isset to four and from t=4T the tap coefficient calculation starts.

[0151] Herein if an attempt should be made to output a filter outputy(3T) then t=−T needs to be entered to the most rightward tap. However,−T does not exist and y(3T) cannot be output. As such for t=0 to 3T nofilter output can be obtained and accordingly from t=4T the calculationstarts.

[0152] In accordance with the counter's counted value a receive signalsymbol of 0T to 8T of the signal stream of the antenna of interestdesignated by ANT is input to a filter by nine taps (step S45).

[0153] The adaptive array's reception weight vector calculator uses anminimum mean square error (MMSE) based on a square of an error to updatea weight, i.e., provide a weight learning. More specifically, thereception weight vector calculator em ploys weight updating algorithmsfor example the aforementioned RLS algorithm employing the MMSE, as wellas a least mean squares (LMS) algorithm.

[0154] The weight updating algorithm is categorized mainly into thefollowing two types: the first weight updating algorithm, such as theRLS algorithm, iterates a calculation less frequently so that a weightconverges rapidly and a targeted value is rapidly approached (forexample with approximately 10 symbols a weight converges). However, itis more susceptible to noise and other disturbance. By contrast, thesecond weight updating algorithm, such as the LMS algorithm, iterates acalculation more frequently so that a weight converges slowly and a longperiod of time is required before a targeted value is arrived at(converging a weight requires a large number of symbols (e.g.,approximately 100 symbols)). However, it is less susceptible to noiseand other disturbance.

[0155] Such an adaptive array's processing technique using the MMSE andthe RLS and LMS algorithms using the MMSE are well known techniques, ashas been described previously, and disclosed by Nobuyoshi Kikuma,Adaptive Signal Processing by Array Antenna, Kagaku Gijutsu Shuppan, pp.35-49, “Chapter 3 MMSE Adaptive Array,” as has been mentionedpreviously. Accordingly, they will not be described herein.

[0156] Although the algorithms are such different as described above,weights minimizing (nulling) an MSE of an error signal in the FIG. 14adaptive array converge generally at a single value.

[0157] In the present embodiment a tap coefficient is calculated by amethod initially using both the RLS and LMS algorithms to allow a weight(a tap coefficient) to rapidly approach a targeted value and then usingthe LMS algorithm to allow the weight to slowly converge at the targetedvalue. Using a 9-tap adaptive array, a weight is converged each time tominimize an MSE, and a finally determined one is adopted as a tapcoefficient of a correction filter.

[0158] Accordingly in step S46 a decision is made as to whetheriteration I has reached five. If not an adaptive array processing withthe RLS and LMS algorithms alternately switched is employed to calculatea filter coefficient. If iteration I is five or more then an adaptivearray processing by the LMS algorithm alone is employed to calculate afilter coefficient.

[0159] More specifically, if iteration I is less than five (step S46) a9-tap adaptive array processing by the RLS and LMS algorithms isperformed to provide a rapid convergence at an optimal tap coefficient.

[0160] Initially at step S47 a correlation matrix's inverse matrix isinitialized and then at step S48 an RLS reference signal is used toallow the RLS algorithm to converge a tap coefficient. This is repeateduntil a decision is made at step S49 that the number of symbols of areceived signal has attained 12 (i.e., within an RLS reference signalsection). More specifically, it is repeated while at step S50 the numberof symbols is incremented by one (an input to the 9-tap adaptive arrayis shifted by one symbol).

[0161] If a decision is made at step S49 that the number of symbols hasarrived at 12 then until a decision is made at step S55 that the numberof symbols has arrived at 106 the number of symbols is incremented byone (step S56), while a processing in an LMS reference signal-freesection of the 9-tap adaptive array is provided (step S54).

[0162] In this section, a reference signal held in memory 10 is not usedand, as described hereinafter, the LMS algorithm is used to converge atap coefficient.

[0163] Typically, a signal used for example by the PHS for communicationhas a true signal point at any of signal reference points of π/4 shiftquadrature phase shift keying (QPSK) at each symbol point at any time.However, a received signal's I, Q phase does not converge at a π/4 shiftQPSK signal reference point due to interference or the like.

[0164] As has been described above, in a section of a received signalthat has a reference signal the received signal and the reference signalare used to effect a weight learning. In a section free of a referencesignal, a phase difference between a sum of complex multiplications of areceived signal by a weight vector calculated one symbol before and aπ/4 shift QPSK signal reference point is used as an error in providing aweight learning.

[0165] Accordingly, the reference signal is calculated by a reverseoperation from the weight vector one symbol before, and from the signalpoint's I, Q signal a shortest π/4 shift QPSK signal point is selectedand signal d(t) is brought to the signal reference point. As thereference signal thus obtained is used in place of a reference signalpreviously held in memory, it will be referred to as a representativesignal for the sake of illustration. At step S54, although outside theLMS reference signal section, such a representative signal d(t) is usedto allow the LMS algorithm to converge a tap coefficient.

[0166] Note that adaptive array processing outside such a referencesignal section is specifically described for example in Japanese PatentLaying-Open No. 2001-144825. Accordingly it will not be described.

[0167] Then if a decision is made at step S55 that the number of symbolshas arrived at 106 then a decision is made at step S57 whether iterationI exceeds 20 and if not then at step S58 iteration I is incremented byone and step S44 and the subsequent steps are repeated.

[0168] In particular, if a decision is made at step S46 that iteration Iis five or more then the 9-tap adaptive array processing only by the LMSalgorithm is used to provide convergence at an optimal tap coefficient.

[0169] Initially at step S51 an LMS reference signal is used and the LMSalgorithm is employed to converge a tap coefficient. This is repeateduntil a decision is made at step S52 that the number of symbols of areceived signal has attained 12 (i.e., within an LMS reference signalsection). More specifically, it is repeated while at step S53 the numberof symbols is incremented by one (an input to the 9-tap adaptive arrayis shifted by one symbol).

[0170] If a decision is made at step S52 that the number of symbols hasarrived at 12 then until a decision is made at step S55 that the numberof symbols has arrived at 106 the number of symbols is incremented byone (step S56), while a processing in an LMS reference signal-freesection of the 9-tap adaptive array is provided (step S54).

[0171] In this section, the above representative signal d(t) is used andthe LMS algorithm is employed to converge a tap coefficient.

[0172] Then if a decision is made at step S55 that the number of symbolshas arrived at 106 then a decision is made at step S57 whether iterationI exceeds 20 and if not then at step S58 iteration I is incremented byone and step S44 and the subsequent steps are repeated.

[0173] If a decision is made at step S57 that iteration I exceeds 20then a decision is made as to whether an MSE with error signal e(t)calculated is no more than a predetermined value (step S59). If so thenat step S60 a finally converged filter coefficient of a signal stream ofthe antenna of interest is recorded and until a decision is made at stepS61 that parameter ANT identifying an antenna exceeds three, at step S62parameter ANT is incremented by one, while for all antenna signal pathsa tap coefficient is calculated and recorded.

[0174] Thus for all of the four antenna signal paths filter coefficientsare calculated.

[0175] If despite I exceeding 20 a decision is made at step S59 that anMSE is not no less than a predetermined value, a decision is made thattap coefficient convergence has failed and at step S66 an error flag isset and at that time point the tap coefficient calculation isterminated.

[0176]FIG. 13 shows an exemplary variation of a method of calculating atap coefficient shown in FIGS. 10-12. This exemplary variation is apartial variation of the FIG. 12 processing and the remainder is thesame as described with reference to FIGS. 10 and 11 and accordingly willneither shown or described.

[0177]FIG. 13 corresponds to FIG. 12, except that the former includesthe latter's steps S57 and S59 switched in order. More specifically, inthe FIG. 13 example, the step S57 decision on whether iteration Iexceeds 20 is preceded by the step S59 decision on whether an MSE is nomore than a predetermined value. More specifically, if I is less than 20and an MSE is sufficiently small, i.e., a weight (a tap coefficient)sufficiently converges, then without waiting for 1 to exceed 20 theprocess exits the I iteration loop and at step S60 a finally convergedtap coefficient is recorded.

[0178] Then until a decision is made at step S61 that parameter ANTidentifying an antenna exceeds three, at step S62 parameter ANT isincremented by one, while for all antenna signal paths a tap coefficientis calculated and recorded.

[0179] If at step S59 a decision is not made that an MSE is no more thanthe predetermined value and in addition at step S57 I exceeds 20 then adecision is made that tap coefficient convergence has failed and at stepS63 an error flag is set and at that time point the tap coefficientcalculation is terminated.

[0180] Thus in accordance with the present invention in a radioapparatus a plurality of filter means digitally compensating for adifference of a characteristic between a plurality of analog circuitssubjecting a signal received at a plurality of antennas to an analogprocessing can be provided subsequent to a corresponding toanalog-digital converter so that distortion in waveform of an input to adigital signal extraction means can be compensated for to prevent thedigital signal extraction means from having an impaired ability toreduce an interference component.

[0181] Furthermore in accordance with the present invention a pluralityof filter means digitally compensating for a difference of acharacteristic between analog circuits can be provided with a filtercoefficient accurately determined for example prior to shipment of aradio apparatus under an ideal condition with a frequency offsetcompensated for and a timing of sampling corrected so that an inputwaveform's distortion can more accurately be compensated for.

[0182] Furthermore in accordance with the present invention a pluralityof filter means digitally compensating for a difference of acharacteristic between analog circuits can be provided with a filtercoefficient accurately determined in a shipped and installed radioapparatus by selecting a satisfactory signal received from a mobileterminal and using the selected signal for calculation.

INDUSTRIAL APPLICABILITY

[0183] In accordance with the present invention a difference of acharacteristic between a plurality of analog circuits can digitally becompensated for so that the present invention is useful in a radioapparatus subjecting a signal received at a plurality of antennas to ananalog processing.

1. A radio apparatus using a plurality of antennas to receive a signal,comprising: a plurality of analog circuits provided to correspond tosaid plurality of antennas and subjecting signals received at saidplurality of antennas, respectively, to an analog signal processing; aplurality of analog-digital converters receiving signals from saidplurality of analog circuits, respectively, to convert said signals todigital signals; a plurality of filter means receiving said digitalsignals from said plurality of analog-digital converters, respectively,to filter said digital signals to compensate for distortion in waveformresulting from a difference of a characteristic between said pluralityof analog circuits; and digital signal extraction means receivingsignals from said plurality of filter means, respectively, to subjectsaid signals to a digital signal processing to extract a receivedsignal.
 2. The radio apparatus according to claim 1, wherein saidplurality of filter means are each a digital filter having acharacteristic to compensate for a difference between a characteristicof said analog circuit corresponding thereto and an ideal circuitcharacteristic.
 3. The radio apparatus according to claim 2, whereinsaid digital filter is an FIR filter.
 4. The radio apparatus accordingto claim 1, wherein said digital signal extraction means is an adaptivearray processing circuit employing an adaptive array processing toextract a received signal.
 5. A method of receiving a signal in a radioapparatus having a plurality of antennas, said radio apparatus includinga plurality of analog circuits provided to correspond to said pluralityof antennas and subjecting signals received at said plurality ofantennas, respectively, to an analog signal processing, and a pluralityof analog-digital converters receiving signals from said plurality ofanalog circuits, respectively, to convert said signals to digitalsignals, the method comprising the steps of: filtering said digitalsignals output from said plurality of analog-digital converters tocompensate for distortion in waveform resulting from a difference of acharacteristic between said plurality of analog circuits; and subjectingsaid filtered digital signals to a digital signal processing to extracta received signal.
 6. The method according to claim 5, wherein the stepof filtering is digital-filtering accompanied by a characteristic forcompensating for a difference between a characteristic of said analogcircuit corresponding thereto and an ideal circuit characteristic. 7.The method according to claim 5, wherein the step of subjecting is aprocessing employing an adaptive array processing to extract a receivedsignal.
 8. A method of measuring a filter coefficient of a radioapparatus using a plurality of antennas to receive a signal, said radioapparatus including a plurality of analog circuits provided tocorrespond to said plurality of antennas and subjecting signals receivedat said plurality of antennas, respectively, to an analog signalprocessing; a plurality of analog-digital converters receiving signalsfrom said plurality of analog circuits, respectively, to convert saidsignals to digital signals; a plurality of filter means receiving saiddigital signals from said plurality of analog-digital converters,respectively, to filter said digital signals to compensate fordistortion in waveform resulting from a difference of a characteristicbetween said plurality of analog circuits; and digital signal extractionmeans receiving signals from said plurality of filter means,respectively, to subject said signals to a digital signal processing toextract a received signal, the method comprising the steps of:determining a transmission frequency compensating for a frequency offsetin said plurality of antennas; determining a sampling-timing allowing asampling error in said analog-digital converter to have an optimalvalue; and calculating a filter coefficient of said filter means from asignal of said transmission frequency determined and saidsampling-timing determined.
 9. The method according to claim 8, whereinsaid plurality of filter means are each a digital filter having acharacteristic to compensate for a difference between a characteristicof said analog circuit corresponding thereto and an ideal circuitcharacteristic.
 10. The method according to claim 8, wherein: the stepof determining a transmission frequency includes the steps of allowing atransmit signal of a variable transmission frequency to be received atsaid plurality of antennas, measuring a frequency offset of saidtransmit signal received at said plurality of antennas, and determininga transmission frequency allowing said measured frequency offset to haveno more than a predetermined value; and the step of determining asampling-timing includes the steps of allowing a transmit signal to bereceived at said plurality of antennas; sequentially varying asampling-timing at said analog-digital converter, for each saidsampling-timing varied, measuring and storing a sampling error of areceived signal extracted by said digital signal extraction means, anddetermining a sampling-timing allowing said sampling error to beminimized.
 11. The method according to claim 8, wherein the step ofcalculating a filter coefficient includes the steps of: allowing asignal of said determined transmission frequency to be received at eachof said plurality of antennas; and subjecting a symbol of said receivedsignal to an adaptive array processing as a tap input to calculate afilter coefficient corresponding to a respective tap input.
 12. Themethod according to claim 8, wherein said digital signal extractionmeans is an adaptive array processing circuit employing an adaptivearray processing to extract a received signal.
 13. A method of measuringa filter coefficient of a radio apparatus using a plurality of antennasto receive a signal, said radio apparatus including a plurality ofanalog circuits provided to correspond to said plurality of antennas andsubjecting signals received at said plurality of antennas, respectively,to an analog signal processing, a plurality of analog-digital convertersreceiving signals from said plurality of analog circuits, respectively,to convert said signals to digital signals, a plurality of filter meansreceiving said digital signals from said plurality of analog-digitalconverters, respectively, to filter said digital signals to compensatefor distortion in waveform resulting from a difference of acharacteristic between said plurality of analog circuits, and digitalsignal extraction means receiving signals from said plurality of filtermeans, respectively, to subject said signals to a digital signalprocessing to extract a received signal, the method comprising the stepsof: determining whether a signal received from a mobile terminal at saidplurality of antennas satisfies a predetermined condition; holding asignal received from a mobile terminal at said plurality of antennas,the mobile device satisfying said predetermined condition; andcalculating a filter coefficient of said filter means of said signalreceived and held.
 14. The method according to claim 13, wherein saidplurality of filter means are each a digital filter having acharacteristic to compensate for a difference between a characteristicof said analog circuit corresponding thereto and an ideal circuitcharacteristic.
 15. The method according to claim 13, wherein the stepof calculating a filter coefficient includes the step of subjecting asymbol of said held, received signal to an adaptive array processing asa tap input to calculate a filter coefficient corresponding to arespective tap input.
 16. The method according to claim 13, wherein saiddigital signal extraction means is an adaptive array processing circuitemploying an adaptive array processing to extract a received signal. 17.A program to measure a filter coefficient of a radio apparatus using aplurality of antennas to receive a signal, said radio apparatusincluding a plurality of analog circuits provided to correspond to saidplurality of antennas and subjecting signals received at said pluralityof antennas, respectively, to an analog signal processing, a pluralityof analog-digital converters receiving signals from said plurality ofanalog circuits, respectively, to convert said signals to digitalsignals, a plurality of filter means receiving said digital signals fromsaid plurality of analog-digital converters, respectively, to filtersaid digital signals to compensate for distortion in waveform resultingfrom a difference of a characteristic between said plurality of analogcircuits, and digital signal extraction means receiving signals fromsaid plurality of filter means, respectively, to subject said signals toa digital signal processing to extract a received signal, the programcausing a computer to effect the steps of: determining whether a signalreceived from a mobile terminal at said plurality of antennas satisfiesa predetermined condition; holding a signal received from a mobileterminal at said plurality of antennas, the mobile device satisfyingsaid predetermined condition; and calculating a filter coefficient ofsaid filter means of said signal received and held.
 18. The programaccording to claim 17, wherein said plurality of filter means are each adigital filter having a characteristic to compensate for a differencebetween a characteristic of said analog circuit corresponding theretoand an ideal circuit characteristic.
 19. The program according to claim17, wherein the step of calculating a filter coefficient includes thestep of subjecting a symbol of said held, received signal to an adaptivearray processing as a tap input to calculate a filter coefficientcorresponding to a respective tap input.
 20. The program according toclaim 17, wherein said digital signal extraction means is an adaptivearray processing circuit employing an adaptive array processing toextract a received signal.